As I've seen that Overkill Prime, I've started to figure out how to do that with my Prime+Breaker+Wing, finally getting to the conclusion that I can only make it, by letting the Shoulder-Straps of the Galaxy-Cannon upwards till I attached the Wing-Saber-Breastplate, then I flipped them downwards, to hold at least a little onto the Breastplate-parts.

Damn, it would've been very nice, if the Galaxy-Cannon would have fitting holes for WingSaber, that would allow better connection, and slightly changed connectors, that would also allow to attach the Breastplate and the Galaxy-Cannon together without interfering eachother.

As i don't have a second Breaker(Nemesis or Leo), I decided to give him the Blaster from the right-Side into the Left hand, inserted the CyberKey into the Cannon hjust like in the Show, and rotated the Left Leg-Cannon to point in the same Direction.
Also I connected the Cannons from WingSaber to the Feet, and reattached LeoBreakers Tail to it's Beast-mode-Connection, letting it serve optically as a thumb.

As for annother Secret there are some slightly, undocumented transformation-part in the movie Line, like Deluxe Brawls Leg-parts, that have the Tracks can be rotated, to reveal more of the Angular Plates on the front of his Lower-Legs.

Or RiD Optimus Primes blaster can actually be fitted with the Connector into the white Ladder, leaving it useable in Super-Mode.

You just pull back on the treads when he's in robot mode; there shouldn't be that much resistance, it just gives a little click. Have a close look at the legs and you should be able to spot the hinge point.

Energon Skyblast can combine with powerlink Ironhide (when united with Jetfire as legs) - Just open the Jetfire hatches and put Skyblast in vehicle mode face down... Is a great addition to this combined mode (even the Autobot symbols in Skyblast wings make a perfect match)